When was vacuum casting invented?

Vacuum casting, or vacuum duplication with a silicone mold, is the combination of two distinct methods: vacuum casting on the one hand and flexible molds on the other hand. This combination is made possible by the development of silicone resin, the material from which the mold is made. Added to this are polyurethanes, which mimic the properties of the materials used in mass production. This has contributed to the success of this method, now widely used in pre-series productions or small series for visual, assembly, functional, mechanical and market testing.

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History of vacuum casting

The first silicone resins were developed in , but it was not until the s that the technology of plastic vacuum casting using silicone molds was developed in the technical universities of Dresden and Cottbus in the former GDR (German Democratic Republic).

This process is a combination of conventional and well-known technologies: vacuum casting had already long been used, and flexible molds such as natural rubber have also been used for many years by restorers and sculptors to make molds of reliefs or sculptures without damaging them. Silicone resin and its heat resistance properties, in particular, made it possible to combine the two methods to use silicone molds as a method for vacuum casting.

Originally unknown in Europe, the technology was sold to Japan in the s, where it was principally used in the automotive industry. It was then reintroduced in Europe, where it is now used in the R&D departments of almost all major production companies.

In the s, thermosetting plastics were developed, which were then used in vacuum casting. These plastics perfectly mimic the appearance and properties of materials used in mass production, allowing a breakthrough in vacuum duplication using silicone molds. Since the s, based on this concept, other processes, automation, and accessories were developed, guaranteeing simple, fast and cost-effective management of the system, which ensured the success of this method.

Definition of vacuum casting

Vacuum casting or vacuum duplication consists of first creating a model by stereolithography, CNC machining or 3D printing. This model is used to create silicone mold. Once the mold has been made, the molding is performed by vacuum injection, using a vacuum casting machine: a polyurethane resin is injected into the silicone mold using the machine, which cures under the heat. Once the part has cured, the mold is removed and the operation can be repeated several dozen times.

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The value of this technique is the ability to re-use the silicone mold and obtain prototypes perfectly identical to the model, using materials close to the right material. This makes it ideal for pre-series or small-scale productions. The prototypes obtained are completely identical and of very good quality.

There is also a large choice of hardnesses, materials, and even the possibility of painting or dyeing in the mass, or adding an overmolding of inserts. This method is also particularly suited when the geometry of the part is difficult to mold due to the elasticity of the silicone mold. Finally, it is less expensive than molding with a steel mold.

The history of vacuum casting

One of the first relatively simple vacuum casting systems with manual mixing and tilting unit.

During the sixties the technology of plastic casting under vacuum using a silicone mould was developed, at the Technical Universities of Dresden and Cottbus in the former German Democratic Republic.

As no one realised the advantages of the system in Europe, the technology was sold to Japan in the seventies, where it was mainly used in the automotive industry. The curious fact is that from there it came back to Europe and Germany, and meanwhile it can be found in the development department of nearly every large production company.
On principle, this process is the combination of conventional, well-known technologies:

An Italian machine with injection into the vacuum from outside by means of a cartridge gun.

Casting by in-gate and risers has been practiced since the Bronze Age, i.e. since more than 3.500 years. Also vacuum has been used for several thousand years. Cupping, for example, was achieved by means of prepared cow horns, which, after having been attached, were either sucked in with the mouth and sealed with wax, or a vacuum was produced  by burning down  alcohol-soaked wool flakes  within the horn. Flexible moulds, for example made of natural caoutchouc, have also been used for many years, by restorers and sculptors among others, in order to make moulds of reliefs or sculptures  without disturbing them.
This Japanese machine with the characteristic bull&#;s-eyes is the precursor of all modern vacuum casting systems.
The combination of these three techniques in conjunction with thermosetting plastics, which were developed in the eighties, represents the main advantage of this procedure. It led to the breakthrough, allowing the two-component-resins, to imitate materials used in large series production as polypropylene and polyethylene in a practically identical way.
Based on this concept, further processes, automation and accessories were developed, which guaranteed a simple, fast and cost effective handling of the system.